Photolithography is a critical and frequently used operation in the manufacture of semiconductor devices. Each semiconductor device undergoes multiple photolithography operations which form the patterns that transform layers of material into interconnected circuits. Each photolithography operation includes an operation that coats the substrates with a photoresist material and a develop operation that develops the exposed and patterned photoresist layer by coating the substrate with a developer. Photolithography operations may also utilize additional coating operations such as operations that coat the substrates with anti-reflective coatings, ARC's, adhesion promoters, and various other coatings. Each photolithography operation therefore includes multiple coating operations that dispense a photolithography fluid onto a substrate that is rotated to produce a coating on the substrate surface.
The manufacturing tools that are used to coat the substrates include a dispense port at which the fluid is introduced to the substrate, which is rotated to produce a very thin coating on the substrate. It is critical for the coating to include a thickness that is uniform and lies within a narrow range of acceptable thicknesses prescribed by the specification. It is also critical to obtain the desired thickness of the coated material from a corresponding amount of dispensed material because the fluids used in the various photolithography coating operations are very expensive and it would be cost prohibitive to dispense excess amounts of fluid that are simply expelled from the substrate when it is rotated, i.e. wasted. It is also important to assure that each coating operation results in a high quality coating. If there are voids in the layer coated on the substrate, if the coating is of non-uniform thickness, or if there are particles contaminating and distorting the coated film, the substrate must be reworked at considerable expense. The rework procedure is also time consuming and delays cycle time.
As such, it is critical to ensure that the fluid such as photoresist or developer, that is dispensed from the dispense port is free of particles and air bubbles and is a clean and homogeneous fluid. For this reason, each photolithography coating tool used to coat the aforementioned materials, advantageously includes a filter that filters the fluid between the fluid reservoir and the dispense port. The filters trap particles, air bubbles and other anomalies that may be included within the photolithography fluid in raw form in the reservoir. The filters must be changed on a regular basis and the associated maintenance requires a requalification of the filter and the fluid dispensing system before the tool can again be used for production runs.
The filter is, of course, porous in nature so that the fluid can pass through the filter while any particles or other anomalies will remain trapped in the filter. Various porous materials such as porous polyethylene, nylon and other suitable materials may be used as the porous filter material for photoresist filters, for example. The filter is typically retained in a filter housing through which the photolithography fluid flows. Various housing configurations are available and the housing may include an inlet port and an outlet port and often includes a purge port. When the photolithography fluid is first passed through a newly installed filter, the filter does not immediately saturate with fluid. Rather, air bubbles are created in the filter as small amounts of air remain trapped within the filter media due to the surface tension of the air bubbles adhering to the porous filter.
The bubbles often remain in the filter for an extended time and are difficult to remove. It is important to remove the bubbles from the filter. Otherwise, the bubbles will become disengaged during production operations, and delivered to the dispense port where they cause problems such as voids in the coated film, when dispensed onto the substrate. Furthermore, the bubbles act as a compressible volume which affects pump operation, adversely affecting the coating operation.
According to one conventional technique, the photolithography fluid is continuously purged through the filter for an extended time until no further bubbles are detected in the outlet line of the filter housing. While this time-consuming qualification process is underway, the tool is not available for production activity and considerable amounts of the photolithography fluid are being wasted while waiting for all of the bubbles to become disengaged from the filter. The wasted photolithography fluid represents a considerable expense, and the unavailability of the tool represents another expense.
Even during normal and continuous use, bubbles can be introduced by being drawn into the filter or as a result of outgassing or due to unconventional surface tension properties of the photolithography fluid. These bubbles also require purging using the same techniques as described supra, and which include the same shortcomings.
The present disclosure addresses these shortcomings.